Heretofore, in the production of warm fluids such as petroleum gas and/or petroleum liquid from a wellbore in the earth through a permafrost zone whereby part of the permafrost could be melted upon continued exposure to heat from the warm fluid, it has been proposed to employ double-walled pipes to provide thermal insulation between the warm fluid passing through the well and the permafrost in the wall of the well. A good background reference in this area is U.S. Pat. No. 3,680,631, the disclosure of which is incorporated herein by reference.
It has been proposed to use a diaphragm connection means which is very small in size,e.g., e.g, one-sixteenth inch in thickness, to minimize the heat loss through this connector since the connector does provide a metallic contact between the inner and outer pipes of the assembly. However, such a thin connector is weak and has a disadvantage of providing a nonrigid assembly. A nonrigid assembly is more prone to damage and even failure during handling, installation, and/or use in the well because the connection can plastically deform under the stresses that normally accompany such activities.
It has now been found that connector means of sufficient size and strength to form an essentially rigid assembly which will not plastically deform under the normal stresses to which the assembly is subjected can be employed without intolerable heat loss.